Control system for balancing hoist

ABSTRACT

A control system for a pneumatically operated balancing hoist in which a load attached to the hoist cable is balanced by regulating air pressure acting on the piston of an expansible chamber hoist motor. The control system is characterized by a pneumatic control circuit including a pressure regulating valve which has a sensor operable to sense the pressure in the hoist motor chamber required to balance a load and set the regulator valve to maintain the load balancing pressure value. The control circuit also includes a pneumatically operated valve which limits the flow of compressed air to the hoist motor to prevent rapid wind-up of the hoist cable. A further feature of the control system includes a circuit arrangement in which the hoist motor exhaust valve is operable to exhaust pressure air from the motor chamber only in response to receiving a positive pressure signal from a pendant hoist controller.

United States Patent 1 1 Workman, Jr. et al.

1 51 Sept. 11, 1973 CONTROL SYSTEM FOR BALANCING HOlST [73] Assignee: Gardener-ljenverCompany,

Quincy, Ill.

[22] Filed: Nov. 18, 1970 [21] Appl. No.: 90,499

Primary ExaminerEvon C. Blunk. Assistant Examiner-James W. Miller Attorney-Michael E. Martin [57] ABSTRACT A control system for a pneumatically operated balancing hoist in which a load attached to the hoist cable is balanced by regulating air pressure acting on the piston of an expansible chamber hoist motor. The control system is characterized by a pneumatic control circuit including a pressure regulating valve which has a sensor operable to sense the pressure in the. hoist motor chamber required to balance a load and set the regulator valve to maintain the load balancing pressure value. The control circuit also includes a pneumatically oper' ated valve which limits the flow of compressed air to the hoist motor to prevent rapid wind-up of the hoist cable. A further feature of the control system includes a circuit arrangement in which the hoist motor exhaust valve is operable to exhaust pressure air from the motor chamber only in response to receiving a positive pressure signal from a pendant hoist controller.

6 Claims, 3'Drawing Figures BACKGROUND OF THE INVENTION Conventional balancing hoists are generally characterized by a pressure fluid operated motor including a piston disposed in an expansible chamber and suitably connected to a rotatable cable drum. A load attached to the hoist cable is raised, lowered, or held in balance by controlling the pressure of the fluid admitted to the hoist chamber and acting on the piston. Such hoists are operable to provide for manual raising and lowering of a balanced load with minimum effort by regulating fluid pressure acting on the piston to a value SUffICI6III to offset the weight of the load. The hoist operator is thereby able to manipulate the load, including raising and lowering it, with a force which is a mere fraction of the actual weight of the load.

Known types of fluid operated balancing hoists usually include a control system which has a self-relieving pressure regulator valve for maintaining pressure in the hoist motor chamber to balance the load. Typical prior art balancing hoist control systems such as disclosed in U.S. Pat. Nos. 2,939,431; 3,260,508; and 3,457,837 use pilot pressure fluid controlled regulating valves wherein the balance pressure in the hoist motor chamber is selected by varying the pilot pressure value which in turn controls the setting of the pressure regulator. The pilot pressure fluid is usually supplied by a controllable pilot pressure regulator and the pilot pressure value is controlled by changing the setting of the pilot pressure regulator or by bleeding pilot pressure fluid, normally compressed air, from downstream of pilot pressure regulator by means of a manual valve controlled by the hoist operator.

In many applications of balancing hoists the weight of the load is subject to change or loads of different weights are successively hoisted and balanced. In prior art balancing hoist controls load weight variations are required to be compensated for by the hoist operator changing the pressure setting of the regulator valve by bleeding air from downstream of the pilot pressure regulator or resetting the pilot pressure regulator itself. If a pilot pressure regulator is not used, the hoist chamber pressure regulator is required to be manually reset by the hoist operator. This operation is time consuming and subject to inaccurate adjustments resulting in poor productivity on job applications using balancing hoists. The aforementioned U.S. Pat. No. 2,939,431 discloses a balancing hoist control system which automatically senses the pressure required to balance a particular load by trapping a small quantity of air at the balance pressure in the pressure chamber of separate pressure regulating and pressure relief valves. This system has been found, in practice, to have deficiencies due to leakage of the trapped air quantities resulting in unwanted changes in the balance pressure setting.

Another longstanding problem in balancing hoist controls concerns the danger of having the hoist cable reel up in a rapid and violent manner if a load is dropped or the hoist is operated to reel up the cable without a load attached to the hook.. This dangerous occurrence results from the relatively uncontrolled admission of pressure fluid to the hoist motor chamber causing the piston to rapidly rotate the cable drum.

Prior art control systems of the aforementioned type are usually mounted on the hoist housing and are operator controlled from a pendant type control handle having flexible fluid conductors leading from he control handle to the hoist proper. As these flexible conductors are often subject to damage or to beingsevered, it is accordingly undesirable to have any arrangement of control circuitry which will permit the load to drop due to loss of hoist chamber pressure should the flexible conduits be severed or damaged.

SUMMARY OF THE INVENTION In the present invention there is provided a control system for a fluid operated balancing hoist which is operable to provide for raising, lowering, and automatically balancing a load of any weight up to the capacity of the hoist proper. By providing a control circuit having a pressure regulating valve which is operable to sense the pressure in the hoist motor chamber required to balance the load and automatically adjust itself to maintain the balance pressure value loads of varying weights may be balanced without time consuming adjustment of the controls. Moreover, the control circuit of the present invention includes a pressure regulator which automatically senses the balance pressure and is operable to be positively locked at the balance pressure setting.

The present invention also provides a control system for a balancing hoist which is operable to prevent rapid and uncontrolled wind-up of the hoist cable in the event of operation of the control system to raise a very light load or if no load is attached to the hoist cable. By including a pressure responsive flow control in the supply passage to the hoist motor chamber which senses pressure in the chamber, unrestricted flow of pressure fluid to the chamber is provided only when the balance pressure value is sufficiently great to indicate a substantial load is being lifted.

The present invention further provides a control system for a fluid operated balancing hoist which includes a pendant controller attached to a control valve module mounted'on the hoist proper by means of flexible fluid conduits. The pendant controller is in circuit with the components of the control system in a manner such that only a positive pressure signal from the controller will operate the balancing hoist to raise or lower a load. Such an arrangement precludes the dropping of a load in the event of damage to the controller or the flexible conduits.

As may be appreciated from the disclosure set forth herein, the present invention provides a control system for a balancing hoist which is safer and more efficient than controls heretofore known.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a longitudinal vertical section of a pressure fluid operated balancing hoist utilizing the control system of the present invention.

FIG. 2 is a schematic representation of the balancing hoist control system of the present invention.

FIG. 3 is a longitudinal section of the hoist motor pressure regulating valve shown schematically in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 there is illustrated a fluid operated balancing hoist generally designated by the numeral 10. The hoist 10 includes a frame 12 adapted to be supported by a hoist trolley 14 which in turn is movably mounted on a trolley beam or rail 16. The hoist is useful in many industrial applications wherein hoisting and manipulation of heavy tools or workpieces is required. The hoist frame 12 includes a stationary shaft member 18 which rotatably supports a cable drum 20 on bearings 22 and 24. The cable drum 20 includes a helically formed groove 26 adapted to wind a flexible cable 28 or the like thereon. The free end of the cable 28 is attached to a suitable hook 30 for attaching a load 32 to the hoist.

The cable drum 20 is formed to have a hollow interior in which is located an expansible chamber hoist motor comprising a movable piston 34 forming an expansible chamber 36 together with the end wall 38 and cylindrical wall portion 40 of the drum. The piston 34 includes axially extending pillars 42 which are adapted to rotatably support roller elements 44. The rollers 44 are each engageable with a rotatable cam 46 having a circular cam track or surface 48. The cams 46 are rotatably mounted on stub shafts 50 which are attached to the end wall 52 of the cable drum 20. The cams 46 also include integrally formed gear teeth 54 and are spaced around the shaft 18 whereby the gear teeth on each cam are engaged with gear teeth 56 formed on the shaft. The cams 46 and respective cooperating rollers 44 are equally spaced around the shaft 18 and are suitably three in number although only two are shown in the sectional view of FIG. 1.

The balancing hoist 10 is operable to raise, lower, or balance a load attached to the hook 30 in response to the supply or venting of pressure fluid, such as compressed air, with respect to the expansible chamber 36. For example, pressure air supplied to the chamber will act on the piston 34 to move the same toward the end wall 52 which will cause rollers 44 to rotate the cams 46 as they roll along the cam surfaces 48. Due to the fact that the gear teeth on the cams 46 are engaged with the stationary gear teeth on the shaft 18, the cams will also be forced to rotate or orbit about the shaft which action accordingly will cause the cable drum 20 to rotate to wind the cable 28 thereon. By supplying pressure air to the chamber 36 at a pressure which will offset the weight of the load tending to unwind the cable and move the piston toward the end wall 38, a load may be suspended in balance at any position within the capability of the hoist. It follows accordingly that venting pressure air from the chamber 36 will allow the load to unwind the cable, rotating the drum and causing the piston 34 to move toward the end wall 38 reducing the volume of the chamber 36.

Pressure air is communicated to and from the hoist motor chamber 36 by means of passages 58 and passage 60 in the shaft 18. The passage 60 is in communication with a control system for the hoist 10 comprising a control module 62 mounted on the side of the frame 12. The module 62 includes two plate-like members 64 and 66 having a gasket 68 interposed therebetween. The member 66 includes a plurality of pressure fluid control valves mounted thereon comprising a control system for the hoist 10. The control system in its entirety is represented by the schematic of FIG. 2. The control valve components are mounted on the member 66 and are suitably interconnected by means of passages internally formed in the members 64 and 66 and by the gasket 68 sandwiched therebetween. Such an arrangement of pneumatic control circuit components is generally well known and therefore it is believed that the schematic representation of FIG. 2 is sufficient to enable one skilled in the art to practice the invention.

Also shown in FIG. 1 is a supply conduit 70 leading from a source of pressure air, not shown, to the control module 62. Flexible conduits 72, 74, 92, and 102 are illustrated depending from the module 62 whence they lead to a suitable hand-held controller 76 whereby a hoist operator may control the operation of the hoist l0.

Referring to FIG. 2 the hoist control system of the present invention is represented schematically, in general, by standard symbols for fluid power components. Valves which are operable to be in more than one finite position have position designations of a, b, or c. The control module plate 62 is represented as the enclosure line in FIG. 2. The pressure air supply conduit 70 leads to a filter-moisture separator 78 and through a pressure regulator 80 for supplying air at a constant reduced pressure to the control system. A conduit 72 leads from the regulator 80 to the pendent controller 76, and a line 82 connected to conduit 72 leads to the inlet port of a pressure fluid regulator represented by the valve 84 operable to be in positions a, b, or c as indicated in FIG. 2. The regulating valve 84 includes pressure sensing means comprising an actuator 84b having a piston 85 operable to compress a spring 86 for shifting the valve 84 to position b. The actuator 84b is in communication with the hoist chamber 36 via line 87 which is connected to the passage 60 in the shaft through the opening 88 in plate member 66, see FIG. 1. The pressure sensing actuator 84b is operable to be locked in a given position by a pair of spring biased fliud operated pistons 90 which are connected to a fluid line 92 leading to the controller 76.

The regulating valve 84 is operable to be shifted to position a by a fluid actuator 840 including an adjustable biasing spring. Valve 84 is also operable to be in position 0 which may be determined by adjusting the actuator 840 so that the forces acting on thevalve due to the position a and b actuators are in balanced opposition to each other. The construction and operation of an embodiment of the regulating valve 84 is described in further detail herein with regard to FIG. 3 of the drawings. In position a of the regulating valve 84 the line 94 is operable to be vented through the adjustable restriction 96 to atmosphere. In position b the regulating valve 84 is operable to supply pressure fluid to line 94 and through two-position valves 97, 98 and 99 to line 87 to supply fluid to the hoist chamber 36. Valve 97 is operable to be in position a except when a pressure signal is supplied thereto from line 100 leading from the controller line 74. In position b of valve 97 line 94 is blocked and the position a actuator of regulating valve 84 is vented to atmosphere. Valve 99 is operable to be in position a connecting line 94 with line 87 except when a pressure fluid signal supplied from line 102 by way of the controller 76 operates to shift valve 99 to position b to exhaust or vent the hoist chamber 36 through exhaust line 104, the latter including the variable restriction 106.

A two-position valve 108 is also connected to exhaust line 104 and in position a is blocked. Position b of valve 108 is obtained when a pressure signal is supplied to the locking pistons 90 which position then places the exhaust line 104 in communication with a comparatively unrestricted exhaust line 110. The variable restriction 106 may be adjusted to provide for gradual venting of the hoist chamber 36 when valve 99 only is actuated to position b. However, for rapid venting of the hoist chamber both valves 99 and 108 are actuated to position b.

Valve 98 is primarily a flow control means and is operable to permit fluid flow therethrough in either position a or b. However, in position a a variable restriction limits the flow rate through the valve to a quantity less than that provided if the valve is in position b. Valve 98 will shift to position b only in response to receiving a pressure signal from the hoist chamber 36 via line 87 great enough to overcome the bias of the position a adjustable spring actuator 98a.

The control system illustrated in FIG. 2 also includes the controller 76 which includes manually operated two-position valves 112, 114, 116, and 118 each spring biased to be in position a. The valves 112 and 114 are operable to be actuated to their respective positions b by an actuating lever 120. The valves 112 and 114 are intended to be so arranged that the hoist operator may move lever 120 a predetermined amount to actuate valve 112 only to its position b and by moving lever 120 a further amount actuate valve 114 to its position b with valve 112 also remaining in position b. Valves 116 and 118 are independently operable to be actuated to their position b. However, valve 118 is dependent on valve 116 being in position b to supply pressure fluid to valve 118.

Referring to FIG. 3, an embodiment of the pressure regulating valve 84 is illustrated in longitudinal section. The regulating valve 84 includes a body 122 having a longitudinal bore 124 in which is located a tubular sleeve 126. The body 122 also includes passages 128, 130 and 132 which are respectively in communication with the lines 82, 94 and 95, shown on the schematic of FIG. 2. The sleeve 126 comprises suitable openings in communication with the passages 128, 130 and 132 as shown in H6. 3. Annular O-ring seals 134 prevent unwanted leakage between the sleeve and the bore 124. Slidably housed in close fitting relationship within the sleeve 126 is a valve spool 136 having a reduced diameter section forming a chamber 138. The spool 136 is axially slidable in the sleeve 126 to alternately place passages 128 and 130 or 130 and 132 in communication with each other through chamber 138 or, as shown in FIG. 3, the spool 136 is operable to block passages 128 and 132 simultaneously.

The sleeve 126 is held in position within the valve body 122 by means of a spacer 140 and an end cover 142. The spacer 140 includes passages 144 opening into the area 146 for admitting pressure fluid to act on the end face 148 of the spool 136. A coil spring 150 is also engaged with the spool 136 and an adjusting memher 152 having a portion threadedly engaged with the end cover 142. A nut 154 is operable to lock the member 152 in a predetermined position whereby a predetermined biasing force may be exerted on the spool 136 by the spring 150.

The passages 144 in the spacer 140 are suitably in communication with line 188 which, by way of valve 97 in position a, is connected to line 94, see FIG. 2.

The spool 136 includes a portion 156 extending into the area 158 in the valve body. The portion 156 is engaged by the biasing spring 86 which in turn is supported by an elongated cylindrical member 160 comprising the pressure sensing means 84b shown schematically in FIG. 2. The member 160 includes a stern 162 engageable with the piston slidably housed in a sleeve 16 1. The piston 85 includes a pressure surface 166 operable to be acted on by pressure fluid admitted by suitable passage means, not shown, to the chamber 168 formed by the sleeve 164 and the end cover 170. The chamber 168 is in communication with the hoist chamber 36 by way of line 87, FIG. 2, and a suitable passage, not shown, in valve body 122. In response to the admission of pressure fluid to the chamber 168 from the hoist chamber, the piston 85 operates to move the member 160 to compress the spring 86 and force the spool 136 to move toward the end cover 142 against the bias of spring 150.

The position of the member 160 can be controlled by mechanical locking means comprising the opposed spring biased pistons each including a shoe 172 operable to grip the exterior surface 174 of the member to frictionally hold said member in a predetermined position. The pistons 90 are suitably housed in the stepped bores 176 forming pressure chambers 178. In response to the admission of pressure fluid to the chambers 178 to act on the pressure surfaces 180 the pistons 90 are operable to move against the bias of springs 173 to release the gripping action of the shoes 172 on the member 160 whereby the position of the member 160 may be determined by the biasing forces due to pressure fluid acting on the piston 85 and the spool 136 as well as the forces of springs 86 and 150. The chambers 178 are in communication with line 92, of FIG. 2, by means of suitable passages, not shown, in the valve body 122. The pistons are retained in the stepped bores 176 by means of covers 182 fastened to the valve body. The covers 182 have openings 185 for venting chambers 187.

The regulating valve 84 shown schematically in FIG. 2 has a position b actuator 84b referred to as the pressure sensing means and in the embodiment of FIG. 3 comprises the piston 85, member 160 and spring 86. The position a actuator 84a represented in FIG. 2 comprises the end face 148 on the valve spool and the adjustable spring 150 in the FIG. 3 embodiment of the regulating valve.

In use with the hoist control system illustrated in FIG. 2 the pressure regulating valve 84 operates to regulate the pressure in the hoist chamber 36 to a constant value to keep the hoist load in balance. In. use with the system of FIG. 2 the valve 84 is set at the regulating pressure by supplying pressure air to the chambers 178 to release the member 160. Pressure air from the hoist chamber 36 acting on piston face 166 will move the spool 136 toward the end cover 142 in opposition to the bias of spring 150 and also compressing spring 86. Depending on the pressure force exerted on the piston 85 the spool may move to engage the spacer 140. Upon establishing the biasing force created by the pressure in chamber 168 pressure air is vented from chambers 178 allowing the pistons 90 to be spring biased to lock the member 160 in a predetermined position. Pressure air from the hoist chamber 36 is then admitted to the area 146 to act on the face 148 of the spool providing a force tending to move the spool to further compress spring 86. By an initial suitable adjustment of spring 151) a force sufficient to reposition the spool 136 to balance position shown in FIG. 3 may be obtained for all pressure values necessary to balance a load on the hoist 1b. The position of valve spool 136 shown in FIG. 3 corresponds to the position 0 of the schematic representation of the regulating valve of FIG. 2, which position the valve assumes when the load is balanced and not moving. In response to changes in volume of the hoist chamber 36 the pressure therein and acting on the spool end face 148 changes and the spool 136 moves to connect the passage 130 to passage 132 thereby venting air from the chamber 36 or the spool moves oppositely to connect passage 130 with passage 128 to supply air to the hoist chamber. The operation of the regulating valve 84 will be further described in the description of the operation of the hoist control system set forth herein.

As previously stated thecontrol system illustrated in FIG. 2 together with the regulating valve embodiment of FIG. 3 may be used to operate the balancing hoist to raise, lower, or balance a load attached to the hoist cable 28. With pressure air supplied to the control system through conduit 70 the hoist may be operated to raise a load by moving lever 120 on the controller to shift valve 112 to position b. This action will cause pressure air to flow through conduit 74 and valves 98 and 99 both in position a to the hoist chamber 36 to cause the piston 34 to rotate drum 20. With a load attached to the hoistcable the pressure in hoist chamber'36 will increase rapidly and valve 98, sensing the pressure increase, will shift to position b providing for comparatively unrestricted flow of air to the-chamber for raising the load at a suitable rate. The pressure at which valve 98 shifts from the restricted flow position a to position b may be varied by the adjustable spring actuator 98a. If no load were attached to the hoist cable, the piston 34 would move with very little resistance and, accordingly, with only a small pressure increase in chamber 36. Flow to chamber 36 would therefore be restricted as valve 98 would remain in position 0. Therefore, in the event that the hoist was operated to reel up the cable with no load attached thereto, the restricted flow of air provided by the valve 98 remaining in position a would prevent fast reel-up of the cable. Accordingly, damage to the hoist and possible injury to operating personnel would be prevented. While the hoist is being operated to raise a load, pressure air is also supplied to shift valve 97 to position b to vent the actuator 84a of the regulating valve 84. In position b valve 97 also blocks line 94 preventing flow of air from the hoist chamber to the regulating valve 84.

If the hoist operator desires to balance the load being hoisted, the lever 120 is further depressed to shift valve 114 to position b which supplies pressure air through line 92 to shift a self-actuating quick exhaust valve 184 to position a. Pressure air is then also supplied to the chambers 178 of the release pistons 90 releasingthe regulator valve sensor 84b to sense the pressure in the hoist chamber 36. Valve 108 is also shifted to position b but is not operable to rapidly exhaust the hoist chamber as valve 99 has remained in position a. When the desired hoisting distance is reached, lever 120 is released and valves 112 and 114 return to position a. Valve 112 vents line 74 in position a allowing valve 97 to return to position a. Quick exhaust valve 184 shifts itself to position b venting the release chambers 178, FIG. 3, and locking the sensor 84b in a position corresponding to the pressure in the hoist chamber. Check valve 186 prevents line 94 from venting through valve 112. Since valve 94 has returned to position a, actuator 84a of the regulator valve is now pressurized by being in communication with hoist chamber 36 and the regulating valve is balanced in position 0 blocking escape of air from the hoist chamber.

The load is now held in balance and if manual raising of the load is performed, the volume of chamber 36 will increase tending to lower the pressure therein and causing valve 84 to move to position b thereby supplying air to the hoist chamber 36 until the balance pressure is restored. Conversely, if the load is manually lowered, a reduction in the volume of chamber 36 will cause the pressure in chamber 36 to increase and cause valve 84 to tend to shift to position a venting the hoist chamber until the balance pressure is restored. The pressure reguired to move a load during the hoisting operation has been determined to be essentially the same as the balance pressure and slightly less than the pressure required to overcome static friction in the hoist mechanism. Therefore, the pressure sensed by the regulator valve sensor while the load is being raised is essentially the balance pressure. When the lever is released and the air supply to the line 87 is cut off, a very slight pressure drop sufficient to stop the load moving upward occurs due to the expansion of a small amount of air in line 188 and the passages 144 and area 146 of the regulator valve 84. This slight pressure drop is not enough to allow the load to creep downward however, and the load remains balanced.

A load suspended in balance may be lowered by manually actuating valve 116 on the controller to position b supplying air through line 102 to exhaust valve 99. Valve 99 is then shifted to position b providing a controlled venting of the hoist chamber through the variable restriction 106. At any point in the lowering process the load will be stopped and placed in balance upon release of the actuating lever ll6b whereby valve 116 will return to position a. With valve 99 in position a, having vented its position b actuator through valve 116 in position a, the regulator valve 84is again in circuit with the hoist chamber to maintain the balance pressure.

When a load has been lowered to be released it is often desirable to be able to quickly pull the cable slack by hand to facilitate removal of the hook, and slings if used, once the load is at rest. To this end valves 116 and 118 are actuated concurrently to their position b whereby pressure air is supplied to exhaust valves 99 and 108 shifting both to position b to provide a comparatively unrestricted exhaust flow whereby the pressure in the hoist chamber is rapidly reduced to provide little or no resistance to pulling on the hoist cable. Valve 1 18 in position b, assuming valve 116 to be in position b, also operates to supply air to the release chambers 178 releasing the sensing means so that after a load is lowered and disconnected from the hoist cable the regulator valve 84 will not resume its previous setting to supply air at a balance pressure to the hoist chamber. Once the load is lowered and removed pressure in chamber 36 is reduced to zero.

It may be appreciated that the control system of FIG. 2 may be operated to balance different load weights rapidly and efficiently. Any change in load weight may be corrected for by merely momentarily depressing lever 120 to actuate valves 112 and 114 to position b whereby the sensor 84b is released and reset at the pressure in the hoist chamber 36 corresponding to the load weight. The control system of FIG. 2 is also advantageously arranged to prevent catastrophic dropping of the load should the controller 76 be damaged or should the lines leading thereto from the module 62'be cut. Due to the fact that a positive pressure signal from valve 116 is required to operate exhaust valve 99 accidental severing of the line 102 will not affect lowering of the load. Check valves 186 and 190 also prevent venting of the hoist chamber 36 should the air supply fail, or should lines 72 and 74 be damaged.

What is claimed is:

1. A control system for a fluid operated balancing hoist, said balancing hoist including a pressure fluid operated motor having an expansible chamber, means connected to said motor and operable to be connected to a load for raising and balancing said load in response to the operation of said motor, and passage means for conducting pressure fluid to and from said expansible chamber;

said control system including a pressure fluid regulator valve connected to said passage means for supplying pressure fluid to said expansible chamber, said regulator valve including pressure sensing means having a movable actuator in communication with said expansible chamber for sensing the pressure in said expansible chamber and for causing said regulator valve to change said fluid pressure in response to a change in the weight of said load, means for locking said actuator including means for gripping and holding said actuator in a predetermined position for causing said regulator valve to maintain a fluid pressure in said expansible chamber corresponding to a balanced condition of a load connected to said hoist, said means for locking said actuator including fluid operated release means for releasing said actuator to move to cause said regulator valve to change said fluid pressure in response to a change in the weight of said load; and,

said control system includes a controller including valve means for supplying pressure fluid for operating said release means to release said actuator.

2. The invention set forth in claim 1 wherein:

said controller includes valve means including actuating means for supplying pressure fluid to said expansible chamber, and said actuating means is operable to actuate said release valve means to release said actuator concurrently with the supplying of pressure fluid to said expansible chamber.

3. The invention set forth in claim 2 wherein:

said control system includes exhaust valve means connected to said expansible chamber, and said exhaust valve means includes a pressure fluid actuator responsive to pressure fluid being supplied thereto for operating said exhaust valve means to vent pressure fluid from said expansible chamber.

4. The invention set forth in claim 3 wherein:

said controller includes valve means for supplying pressure fluid to said pressure fluid actuator to actuate said exhaust valve means.

5. A control system for a fluid operated balancing hoist, said balancing hoist including a pressure fluid operated motor having an expansible chamber, means connected to said motor and operable to be connected to a load for raising and balancing said load in response to the operation of said motor, and passage means for conducting pressure fluid to said expansible chamber;

said control system including valve means in communication with said passage means for valving pressure fluid to said motor from a pressure fluid supply for raising a load, and flow control means interposed in said passage means between said pressure fluid supply and said motor and including means responsive to a low pressure condition in said expansible chamber for causing said flow control means to limit the flow pressure fluid to said expansible chamber, said means being responsive to an increased pressure condition in said expansible chamber for causing said flow control means to provide substantially unrestricted flow of pressure fluid to said expansible chamber.

6. The invention set forth in claim 5 wherein:

said flow control means comprises valve means movable to be in a first position to limit the flow of pressure fluid to said expansible chamber and a second position to provide substantially unrestricted flow of pressure fluid to said expansible chamber, and said means responsive to said increased pressure condition in said expansible chamber includes actuator means for moving said valve means from said first position to said second position. 

1. A control system for a fluid operated balancing hoist, said balancing hoist including a pressure fluid operated motor having an expansible chamber, means connected to said motor and operable to be connected to a load for raising and balancing said load in response to the operation of said motor, and passage means for conducting pressure fluid to and from said expansible chamber; said control system including a pressure fluid regulator valve connected to said passage means for supplying pressure fluid to said expansible chamber, said regulator valve including pressure sensing means having a movable actuator in communication with said expansible chamber for sensing the pressure in said expansible chamber and for causing said regulator valve to change said fluid pressure in response to a change in the weight of said load, means for locking said actuator including means for gripping and holding said actuator in a predetermined position for causing said regulator valve to maintain a fluid pressure in said expansible chamber corresponding to a balanced condition of a load connected to said hoist, said means for locking said actuator including fluid operated release means for releasing said actuator to move to cause said regulator valve to change said fluid pressure in response to a change in the weight of said load; and, said control system includes a controller including valve means for supplying pressure fluid for operating said release means to release said actuator.
 2. The invention set forth in claim 1 wherein: said controller includes valve means including actuating means for supplying pressure fluid to said expansible chamber, and said actuating means is operable to actuate said release valve means to release said actuator concurrently with the supplying of pressure fluid to said expansible chamber.
 3. The invention set forth in claim 2 wherein: said control system includes exhaust valve means connected to said expansible chamber, and said exhaust valve means includes a pressure fluid actuator responsive to pressure fluid being supplied thereto for operating said exhaust valve means to vent pressure fluid from said expansible chamber.
 4. The invention set forth in claim 3 wherein: said controller includes valve means for supplying pressure fluid to said pressure fluid actuator to actuate said exhaust valve means.
 5. A control system for a fluid operated balancing hoist, said balancing hoist including a pressure fluid operated motor having an expansible chamber, means connected to said motor and operable to be connected to a load for raising and balancing said load in response to the operation of said motor, and passage means for conducting pressure fluid to said expansible chamber; said control system including valve means in communication with said passage means for valving pressure fluid to said motor from a pressure fluid supply for raising a load, and flow control means interposed in said passage means between said pressure fluid supply and said motor and including means responsive to a low pressure condition in said expansible chamber for causing said flow control means to limit the flow pressure fluid to said expansible chamber, said means being responsive to an increased pressure condition in said expansible chamber for causing said flow control means to provide substantially unrestricted flow of pressure fluid to said expansible chamber.
 6. The invention set forth in claim 5 wherein: said flow control means comprises valve means movable to be in a first position to limit the flow of pressure fluid to said expansible chamber and a second position to provide substantially unrestricted flow of pressure fluid to said expansible chamber, and said means responsive to said increased pressure condition in said expansible chamber includes actuator means for moving said valve means from said first position to said second position. 